Friday, February 26, 2016

Resin casting 101: preparing the mold

Perhaps the best part of my recent visit to Jennifer Scott's home was helping her cast a Rajah resin. Because Jenn is awesome, she encouraged me to photograph the entire process so that I could share it here. Thank you so much, Jenn!Rajah is a relatively simple piece, requiring a basic two-piece mold.

The mold is made from silicone rubber, in this case the pink is Smooth On Mold Max 30 and the blue rubber is Smooth On Mold Max XLS-II.

The long "lines" from his chin and feet bottoms are air vents called "sprues." Sprues are necessary to release air from the mold. Without the, trapped air would leave a big gap in the resin cast. The round bumps are "keys" and are designed to fit the mold together and lock it in place. This insures you don't get a slipped seam or a face that has one half higher than the other.

The first step is to spray the mold with mold release. Although you can cast resins without it, the mold release helps preserve the mold. Since molds are expensive and time consuming to make, it's best to baby them as much as possible.

Next, the mold is dusted with baby powder.

This serves two purposes. It helps draw the resin into all the nooks and crannies and gives the resin a nice matte (non-shiny) finish.

Jenn uses a fan brush to spread the baby powder...

paying particular attention to all the tight little crevices around the hair, eyes and ears.

She shakes out excess baby powder...

and then blows on the mold to remove any remaining excess powder.

The goal is to have an almost invisible film of powder evenly coating the entire mold.

When that's done, it's time to cut the support wire. Jenn uses stainless steel wire found in the picture hanging section of a big box hardware store.

Rajah has wire in all four legs and his narrow little tail.

The horse will be upside down during casting, so the wires are shaped to prevent them from fall into the body cavity.

The inside of the mold is now ready for casting. The two pieces are fit together and locked into place by virtue of all those "keys."

Jenn uses two pieces of mica board as her "mother mold." A mother mold is just a hard outer support shell for the soft and flexible silicone rubber. This helps the mold retain its shape so as not to warp or distort the piece being cast.

As an aside, Jenn says at this point, it's always good to stop and check your work desk. If you're missing something, chances are it's strapped to the mold!

The mold is placed inside the casting pot in preparation for the liquid resin.